Synthesis, physical properties, and crystal structure of acetetracenylene-1,2-dione

Article abstract of DOI:10.1246/cl.2011.739

Acetetracenylene-1,2-dione was synthesized by double FriedelCrafts acylation of tetracene with oxalyl chloride in 4654% yield. Photophysical, electrochemical, and thermal analysis of the compound revealed its band gap (E_g = 1.77 eV for the solid state), electron-accepting nature (E _pc ^red = -1.35V vs. Fc/Fc⁺), and thermal stability (T_decomp > 300 °C). Single crystals were successfully grown by physical vapor transport, and parallel π-stacking of the molecules was observed by X-ray crystallography.

Full text of DOI:10.1246/cl.2011.739

doi:10.1246/cl.2011.739
Published on the web June 11, 2011
739
Synthesis, Physical Properties, and Crystal Structure of Acetetracenylene-1,2-dione
³
Toshihiro Okamoto, Tsuyoshi Suzuki, Shungo Kojima, and Yutaka Matsuo*
Department of Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033
(Received April 25, 2011; CL-110346; E-mail: matsuo@chem.s.u-tokyo.ac.jp)
Acetetracenylene-1,2-dione was synthesized by double
O
O
O
O
O
O
Friedel-Crafts acylation of tetracene with oxalyl chloride in
46-54% yield. Photophysical, electrochemical, and thermal
analysis of the compound revealed its band gap (Eg = 1.77 eV
for the solid state), electron-accepting nature (Epcred = ¹1.35 V
vs. Fc/Fc+), and thermal stability (Tdecomp > 300 °C). Single
crystals were successfully grown by physical vapor transport,
and parallel ³-stacking of the molecules was observed by X-ray
crystallography.
acenaphthylene-1,2-dione aceanthrylene-1,2-dione
acetetracenylene-1,2-dione
Figure 1. Diketone derivatives of acenes.
O
O
ClCOCOCl (1.2 equiv)
AlCl3 (2.0 equiv)
Aromatic ketones are important chemicals that have been
widely used in the textile, pharmaceutical, cosmetic, and
agrochemical industries. Among them, diketone derivatives of
acenes are useful intermediates for synthesizing polycyclic
aromatic hydrocarbon derivatives for textile dyes,1 antitumor
agents,2 and bidentate ancillary ligands of polymerization
catalysts.3 The diketone moiety is a versatile starting unit for
preparing useful functionalities such as carboxylic acid anhy-
drides,1 carbodiimides,1 and ¡-diimines,3 which can be used to
control molecular dipole moment, solubility, and HOMO and
LUMO levels to make compounds suitable for practical uses.
Acenaphthylene-1,2-dione (also called acenaphthoquinone) and
aceanthrylene-1,2-dione4 (Figure 1) have been widely used for
such purposes. In particular, aceanthrylene-1,2-dione has re-
ceived special attention as a starting material for constructing
near-infrared dyes5 because it has a more extensive ³-con-
jugated system. Although a much more delocalized ³-system
can be expected to provide richer functionality, acetetracenylene
dione has yet to be synthesized6 and structurally characterized,
likely because of concerns about poor solubility. Herein we
report the synthesis of cyclopenta[fg]tetracene-1,2-dione (ace-
tetracenylene-1,2-dione) (Figure 1), a diketone derivative of
tetracene, as well as its physical properties and X-ray crystal
structure. The present compound can be expected to serve as a
useful intermediate for expanding the above-mentioned appli-
cations.
CH2Cl2
0 °C (6 h) to 20 °C (15 h)
or
1,2-Cl2C6H4, 20 °C (12 h)
Scheme 1. Synthesis of acetetracenylene-1,2-dione.
Figure 2. UV-vis spectra of acetetracenylene-1,2-dione in
CHCl3 (9.2 © 10¹5 M; red line) and in the solid state (properly
diluted with BaSO4; black line).
The synthesis employs double Friedel-Crafts acylation with
oxalyl chloride, which has been reported for preparing acenaph-
thoquinone and aceanthrylene diones.5 We applied this reaction
to tetracene to synthesize the target acetetracenylene-1,2-dione
(Scheme 1). After considerable experimentation, the optimized
reaction conditions were the use of 1.2 molar equivalents of
oxalyl chloride and 2.0 molar equivalents of AlCl3 in CH2Cl2 at
0 °C for 6 h, followed by stirring of the reaction mixture at 20 °C
for 15 h. Most of the tetracene was consumed under the
optimized conditions. After removal of aluminum compounds
by washing with a 9:1 mixture of MeOH and aq. HCl,
purification by sublimation was performed under vacuum
(µ0.007 Torr) at 220 °C for 15 h to obtain the pure target
compound. The chemical yield after sublimation was respectable
(46% yield).7 Alternatively, by using ortho-dichlorobenzene
which has higher solubility for tetracene, the reaction pro-
ceeded in quantitative conversion of tetracene. Under these
conditions, the analytical pure target compound was obtained
in 54% yield without sublimation purification.8 The product
was identified by 1H and 13C NMR, IR spectroscopy
(Figure S117), and elemental analysis. The compound formed
air-stable, black crystals and dissolved in CH2Cl2, CHCl3,
1,2-Cl2C6H4, dimethyl sulfoxide, and other organic solvents to
give a reddish solution.
The photophysical properties of acetetracenylenedione were
investigated by UV-vis and fluorescence spectroscopy. The
UV-vis spectrum in chloroform exhibited absorption maxima at
- = 550 (¾ = 4.4 © 103; onset: - = 585 nm, 2.12 eV), 513
(¾ = 5.9 © 103), and 484 nm (¾ = 4.8 © 103) along with sharp
peaks at 403 (¾ = 1.4 © 104) and 382 nm (¾ = 5.9 © 103)
Chem. Lett. 2011, 40, 739-741
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740
(Figure 2). Absorption of acetetracenylenedione was found to be
red-shifted with ca. 80 nm (absorption maxima) and ca. 100 nm
(onset) from that of aceanthrylene-1,2-dione (Figure S217). In
the solid state, the compound exhibited broad and red-shifted
absorption at - = 575, 533, and 496 nm with a red-shifted onset
value (- = ca. 700 nm). The band gap, Eg, for the solid state
was calculated from the absorption onset to be 1.77 eV. The
compound was not fluorescent.
The electrochemical properties of acetetracenylene-1,2-
dione were investigated by cyclic voltammetry. Oxidation of
the acetetracenylenedione was not observed in the potential
window of dichloromethane, suggesting that the two strongly
electron-withdrawing carbonyl groups result in the tetracene
core being electron-deficient. This compound exhibited an
irreversible reduction wave at Epc = ¹1.35 V and Eonset
=
¹1.25 V vs. Fc/Fc+ in dichloromethane (Figure S317). From
the reduction wave, we roughly estimated the LUMO level to be
¹3.55 eV.9,10 This value is comparable to reported electron-
deficient acenes with fluoro- or cyano substitution.11 In addition,
the value is similar or higher than that of electron-accepting
materials such as fullerene derivatives, C60-bis(indene) adduct
(ICBA, ¹3.63 eV)12,13 and bis(silylmethyl)[60]fullerene (¹3.74
eV),14 which are known to be fullerene-based acceptors with
high-lying LUMO levels and used in organic photovoltaic cells
to obtain high open-circuit voltage.15
Figure 3. Crystal structure of acetetracenylene-1,2-dione.
(a) Ellipsoidal drawing showing the 50% probability level.
(b) Space-filling model. (c) Packing structure viewed along the a
axis. (d) Packing structure viewed along the c axis.
The thermal properties of the acetetracenylenedione were
investigated by thermogravimetry-differential thermal analysis
(TG-DTA) under nitrogen. The compound did not exhibit any
weight loss until 300 °C. A sharp endothermic peak was
observed at 370 °C in the DTA curve (Figure S517). We can
conclude that this compound has sufficient thermal stability,
even under ambient pressure, for various applications.
We thank Mitsubishi Chemical Co. for their financial
support. This research is supported by the Japan Society for
the Promotion of Science (JSPS) through its “Funding Program
for Next Generation World-Leading Researchers.”
References and Notes
Single crystals of acetetracenylene-1,2-dione were prepared
by physical vapor transport using a two-zone (290/190 °C)
electrical heating furnace with atmospheric pressure argon gas
flow (10 mL min¹1). Plate single crystals with metallic luster
grew under these conditions, and the crystals were subjected to
X-ray crystallographic analysis (Figure 3).16 The crystal packing
of the compound consisted of parallel ³-stacking. The inter-
planar distance between tetracene planes was 3.36 ¡, shorter
than the sum of the C£C van der Waals radii (3.40 ¡). The
molecules align to form polar arrays, which are oriented in
an antiparallel manner so that the dipole moments cancel
(Figures 3c and 3d). Such structures are quite different from
the packing structure of a less ³-delocalized compound,
aceanthrylene-1,2-dione, which forms herring-bone packing
(Figure S617).
In conclusion, we successfully carried out double Friedel-
Crafts acylation of tetracene with oxalyl chloride to obtain
acetetracenylene-1,2-dione, which should be a useful intermedi-
ate for further derivatization to produce various fine chemicals.
Compared with known naphthalene and anthracene diketone
derivatives, the present tetracene diketone derivative is expected
to provide richer functionality resulting from its more delocal-
ized ³-conjugated system. We elucidated its photophysical
properties, electron-accepting nature, and thermal stability as
well as its parallel ³-stacking structure. This information will be
useful for not only further functionalization but also application
of the acetetracenylenedione itself in organic thin-film devices.18
Such investigations are underway.
³
1
2
Present address: Department of Advanced Electron Devices,
Institute of Scientific and Industrial Research (ISIR), 8-1
Mihogaoka, Ibaraki, Osaka 567-0047
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Black microcrystals. Melting point was not available due to
sublimation at 300 °C under ambient pressure. 1H NMR
(CDCl3, 500 MHz): ¤ 9.14 (d, J = 9.15 Hz, 2H), 9.04 (s,
2H), 8.18 (d, J = 8.60 Hz, 2H), 7.79 (t, 2H), 7.63 (t, 2H).
13C NMR (CDCl3, 125 MHz): ¤ 188.96, 139.92, 138.69,
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7
¹1
102.79. IR (powder), ¯CO: 1698 cm (s). Anal. Calcd for
Chem. Lett. 2011, 40, 739-741
© 2011 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/

741
C20H10O2: C, 85.09; H, 3.57%. Found: C, 84.81; H, 3.57%.
Details are described in Supporting Information.
LUMO levels were estimated with the following equation:
LUMO level = ¹(4.8 + Eonset) eV.
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8
9
16 Crystal data for acetetracenylene-1,2-dione: monoclinic
space group P21/a, a = 6.8111(1), b = 23.4800(5), c =
8.5200(2) ¡, ¢ = 110.906(1)°, Z = 4, V = 1272.85(4) ¡3.
R = 0.0958 (I > 2·(I)). GOF = 1.464.
10 Aceanthrylene-1,2-dione showed a reversible reduction
wave at E1/2 = 1.39 V vs. Fc/Fc+. Cyclic voltammogram
has been stored in Supporting Information (Figure S4).17
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17 Although there are many reports of aceanthrylene-1,2-dione,
its crystal structure has not been reported. Crystal
data for aceanthrylene-1,2-dione: triclinic space group
ꢀ
P1, a = 8.5161(2), b = 13.1515(2), c = 19.0360(4) ¡,
¡ = 94.8259(8),
Z = 2 (for
¢ = 100.3680(8),
pair of four independent molecules),
£ = 101.4892(8)°,
a
12 A LUMO level has been determined from the first reduction
potential in our investigation with the following equation:
LUMO level = ¹(4.8 + E1/2) eV.
V = 2039.19(6) ¡3. R = 0.0741 (I > 2·(I)). GOF = 0.914.
Detailed structural data are stored in Supporting Information
(synthetic procedures, IR and UV spectra, cyclic voltammo-
gram, and TG-DTA data as well as X-ray crystallographic
data for acetetracenylene-1,2-dione and aceanthrylene-
1,2-dione). Supporting Information is available electroni-
cally on the CSJ-Journal Web site, http://www.csj.jp/
journals/chem-lett/index.html.
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Chem. Lett. 2011, 40, 739-741
© 2011 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/